Local Area Networks (LAN) such as Ethernet or token-ring networks, are generally interconnected through hubs. The hub is a system made of LAN adapters that communicate together through a switch card. The switch card is mainly composed of input ports, output ports and a shared memory.
The data packets received by the input ports are stored into the shared memory at address locations determined by queues containing the packet destination addresses. Then the packets are de-queued to be transmitted to the destination output ports.
Any hardware failure on the switch card is damageable on the data packet transfer, and one common solution to prevent any hardware failure is to duplicate the switch card.
This solution consists in having two switch cards, where one switch is active while the other is backup. During normal operation, both switches operate in parallel meaning that:                they both receive the same commands coming from a Control Point of the switching system;        they both receive the same data packets coming from the LAN adapters;        they both transmit the same data packets. However, the LAN adapters receive the data packets from only the active switch card.        
In case of the active switch card replacement, the backup switch card is substituted to the active one and operates in place of this latter. The LAN adapters then receive the data packets from the newly connected backup switch. When the active switch card is re-activated, a major difficulty is to have the two switches re-synchronized on the same data packets. This problem is not solved in the existing switch systems which admit lost data packets.
Therefore there is a need for a packet loss less system for data packet switch re-synchronization. The present invention offers such system.